Traditional exercise therapy programs for knee osteoarthritis (OA) primarily focus on addressing lower extremity strength and joint motion deficits and have yielded fair to moderate improvements in functional status. Recently, there has been increasing evidence that alterations in lower extremity biomechanical factors during weight bearing activities, such as, alterations in movement and muscle activity patterns, ground reaction forces, and lower extremity loading rates, may have substantial impact on functional status and perhaps progression of disease in individuals with knee OA. Based on these findings, it has been suggested that the effectiveness of exercise therapy programs might be improved by incorporating activities that address altered biomechanical factors. We believe that in addition to strength and joint mobility exercises, incorporating balance and agility training techniques (knee stability training) may improve the effectiveness of exercise therapy by inducing favorable changes in lower extremity biomechanics and allowing for greater improvements in functional status than what can be achieved by strength and joint mobility exercise alone. The overall aim of this project is to test the effectiveness of supplementing traditional exercise therapy with knee stability training techniques, tailored for individuals with knee OA, for improving pain, physical function, and lower extremity biomechanics in individuals with knee OA. We will compare individuals with knee OA who receive a standard exercise therapy program (standard group) to those who receive the same standard program, supplemented with knee stability training techniques (stability training group). The study will be a two group, repeated measures, randomized, blinded clinical trial to compare changes in pain, physical function, lower extremity kinematics, kinetics, and electromyography during gait and a step down task, and changes in spatial/temporal characteristics of gait between subjects with knee OA who receive a standard rehabilitation program and those receiving the same standard program that is supplemented with the knee stability training program. The results of this study will assist in determining whether knee stability training techniques are likely to enhance lower extremity biomechanical and neuromuscular function as well as physical performance and disability over standard training techniques in patients with knee OA. Information gained from this study may improve the ability to refine rehabilitation and prevention programs for individuals with knee OA with the purpose of improving the overall quality of life for individuals with this age related progressive disorder.